Abstract

Two genes (CM-AAT1 and CM-AAT2) with strong
sequence homology (87% identity at the protein level)
putatively involved in the formation of aroma volatile esters
have been isolated from Charentais melon fruit.They
belong to a large and highly divergent family of multifunctional
plant acyl-transferases and show at most 21%
identity to the only other fruit acyl-transferase characterized
so far in strawberry.RT-PCR studies indicated that both
genes were specifically expressed in fruit at increasing rates
in the early and mid phases of ripening.Expression was
severely reduced in ethylene-suppressed antisense ACC
oxidase (AS) fruit and in wild-type (WT) fruit treated with
the ethylene antagonist 1-MCP.Cloning of the two genes in
yeast revealed that the CM-AAT1 protein exhibited alcohol
acyl-transferase activity while no such activity could be
detected for CM-AAT2 despite the strong homology
between the two sequences.CM-AAT 1 was capable of producing esters from a wide range of combinations of
alcohols and acyl-CoAs.The higher the carbon chain of
aliphatic alcohols, the higher the activity.Branched alcohols
were esterified at differential rates depending on the position
of the methyl group and the nature of the acyl donor.
Phenyl and benzoyl alcohols were also good substrates, but
activity varied with the position and size of the aromatic
residue.The cis/trans configuration influenced activity either
positively (2-hexenol) or negatively (3-hexenol).Because
ripening melons evolve the whole range of esters generated
by the recombinant CM-AAT1 protein, we conclude that
CM-AAT1 plays a major role in aroma volatiles formation
in the melon.

Item Type:

Article

Additional Information:

The definitive version is available at http://www3.interscience.wiley.comThe original PDF of the article can be found at European Journal Of Biochemistry website : http://www3.interscience.wiley.com/journal/118906851/abstract